Temperature compensated relay control circuit



AMPERE- TURNS May 5, 1959 A. G. STAVRINAKI 2,

TEMPERATURE COMPENSATED RELAY CONTROL cmcun Filed May 24, 1956 FIG.

FIG. 2 Q

soc AME/E TEMP PR/ WIND/N6 TURNS I B/E PR R) WINDING B- TURNS RESUL TANT(RELAY :0 "c 4,4401 TEMR C AMBIENT nEsuLu/vr ux ME Y A Mi?- TURNS 0-60.8 L0 |.2 T/ME (seam/0s) /NVE/V7 OR y A. 6. STAV/P/NA/(l WQCIQZLTEMPERATURE COMPENSATEDRELAY CONTROL CIRCUIT Alexander G. Stavrinaki,New Y orlr, N.Y., assignor to Bell Telephone Laboratories, Incorporated,New York, N .Y., a corporation of New York 1 Application May 24, 1956,Serial No. 587,056 1 Claim. (Cl. 317-131) This invention relates toelectromagnetic time-delay devices and more particularly to theimprovement of such devices to provide greater constancy in time ofoperation.

The slow-to-operate feature in relay arrangements has been provided inmany ways and among these are devices which employ resistors having arelatively high negative temperature coeflicient of resistance. Suchresistors, whether the temperature coefflcient of resistance be positiveor negative, are normally called and will hereinafter be referred to asthermistors. The temperature and consequently the resistance of athermistor may be altered by the application of an external source ofheat or cold or by electrically energizing the thermistor. One suchtimedelay arrangement has a thermistor in series with the winding of anordinary fast-operate relay and the constants of the circuit, includingthe energizing Voltage, are chosen to limit the initial current in therelay winding to a value which will not cause it to operate; and after aperiod of time, the resistance of the thermistor, under the influence ofthe electrical current, reduces to a critical value to eiiect operationof the relay. In such devices, the period of time between theenergization of the circuit and operation of the relay is dependent uponambient temperature. The time of operation is reduced when the ambienttemperature is above a defined normal and increased when the temperatureis below this normal. Such delay arrangements are thereforeunsatisfactory when a relatively precise time delay is required. Priorarrangements to compensate such circuits for ambient temperature changeshave been bulky and complex as they have utilized an external source ofheat and an insulated box to hold the thermistor at a temperature whichis relatively independent of changes in the ambient temperaturesurrounding the box or have utilized relays having auxiliary switchcontacts along with series and shunt compensating windings.

It is an object of this invention to provide a simple, inexpensivetemperature compensated time-delay relay arrangement which will providea substantially uniform time delay over a relatively large range ofambient operating temperatures.

In accordance with one feature of this invention, standard types offast-operate relays and standard thermistors are connected to provide arelay time-delay device whose operation is substantially independent ofvariations in ambient temperature.

The invention and features thereof will be understood more clearly andfully from the following detailed description with reference to theaccompanying drawings in which:

Fig. l is an exemplary embodiment of the invention; and

Fig. 2 is a graph of the fluxes produced by the relay windings forvarious ambient temperatures.

The time-delay device shown in Fig. 1 consists of an electromagneticrelay having two windings P and S and a set of electrical contacts 11,12, 13, and 14, two

2,885,604 Patented I May 5, 1 959 thermistors T1 and T2 which both havea negative coeflicient of resistance and a standard resistor R1 whichhas a small positive temperature coeflicient of resistance. The relay isof standard design similar to any one of those disclosed in Patents1,652,489, issued to Edward D.'Mead on December 13,1927, and 1,973,090,issued to Daniel D. Miller on September 11, 1934.

' Thermistors T1 and T2 in Patent 2,258,646, issuedto Richard O.Grisdaleon October 14, 1941.

It is to be particularly noted that the thermistor T2 is selected tohave a high initial resistance and a relatively low negative temperaturecoeflicient of resistance; and that the thermistor T1 has a lowerinitial resistance and a higher negative temperature coeflicient ofresistance relative to thermistor T2.

The circuit which comprises the primary winding P of relay 10, the upperback contact 11 and the parallel combination of resistor R1 andthermistor T1 is typical of an uncompensated relay time-delay circuit.The resistor R1 shunting T1 merely alters the temperature resistancecharacteristic of the above series circuit. Curves 21 and 22 in Fig. 2are a graph of the fluxes produced by the primary winding at ambienttemperatures of 10 C. and 50 C., respectively. The secondary winding,which has many more turns than the primary winding, is connected toproduce flux of opposite polarity to that produced by the primary. Thethermistor T2 has an initial high resistance which changes slowly as afunction of temperature. This slow change is apparent from the curves 31and 32 which show the fluxes produced by the secondary winding foroperation at ambient temperatures of 10 C. and 50 C., respectively. Thecurves of Fig. 2 apply where a time delay of four-tenths of a second isrequired between the time the circuit is energized and the time therelay op crates. Although curves 31 and 32 are drawn in the same senseas curves 21 and 22, it should be remembered that these are differentialfluxes and that the net flux at any instance, is the difference betweencurves 21 and 31 or 22 and 352.

The circuit is energized by the closure of switch S. Assuming an ambienttemperature of 10 C., the flux produced by the primary winding willfollow the curve 21 and the differential flux produced by the secondarywinding will follow the curve 31. Four-tenths of a second after switch Sis closed, the critical flux I 10 will result and the relay willoperate. Examination of the resultant flux l 50, which is the differencebetween the fluxes produced by the primary and secondary windings foroperation at 50 C., shows that the critical flux is again reachedfour-tenths of a second after the circuit is energized and that thedelay in operation is substantially independent of ambient temperature.The curves for ambient temperatures lying between 10 C. and 50 C., forboth the primary and secondary fluxes, will lie between the curves shownin Fig. 2 and will have approximately the same character as those shown.Operation of the relay opens the operating path for the primary windingand shunts the high resistance thermistor T2. Therefore, if the relayremains operated long enough for thermistors T1 and T2 to return to thembient temperature, the relay circuit may be released and immediatelyreenergized and a uniform time delay will be incurred.

What is claimed is:

In combination, electromagnetic relay means comprising primary andsecondary windings and electrical contact means controlled byenergization of the relay windings, said secondary winding having manymore turns than said primary Winding, means including switch means forclosing separate and opposing energizing circuits through said windings,each of said circuits including a resistor having a negative temperaturecoeflicient of reare similar to those disclosed 2,885,604 A A f through,a resistor having a low positive temperature coeificient of resistanceshunting said resistor in series with said primary Winding; anorma-lly;closed contactof-saidj 5 congact means; in series; with said primaryWinding,- a

normally open contact of 'said contact means shunting the:

resistor which i.s;-in series -W-ith said secondary Winding, the;resistor; in; series with sa id secondary winding havinga;muchhigherinitial resistance anda lower negative tern-- 10 peraturecoeflicient of resistance than the similar resistor in vseries' withsaid primary: Winding, the resistors: being selected t -haye resistance;temperature characteristics in '4 combination to efiect operation ofsaid contacts at a predetermined; interval of time aftenclosing of said.energiz-. ing circuits substantially independent of variations inambient temperature.

References Cited in the file of this patent UNITED STATES PATENTS

